1. Field
The present invention relates to a circuit board and more particularly to a circuit board on which signal lines adapted to transmit high-speed signals are placed.
2. Description of the Related Art
In recent years, anisotropic conductive film (ACF) interconnection technique has attracted attention as a technique to interconnect circuit boards, such as printed wiring boards (PWB) or flexible printed circuit boards (FPCB).
ACF interconnection technique is one in which the joints of circuit boards are compression-bounded together through an ACF, which is an anisotropic conductive material. The anisotropic conductive material is electrically conductive in the direction of thickness of the joint and nonconductive in the direction of plane of the joint. Such a property of the anisotropic conductive film allows the ACF interconnection technique to be suitable for interconnection of circuit boards that contain fine interconnect lines. For this reason, the ACF interconnection technique has been frequently used in interconnecting a display panel and its associated peripheral portion.
Japanese Unexamined Patent Publication No. 2003-216064 discloses an electro-optical device in which a display board serving as a display panel is connected to a junction board, such as an FPCB, through the ACF interconnection technique.
Recently, in information-processing devices such as personal computers, the use of a high-speed signal interface adapted to transmit signals higher in speed than display signals has begun. For this reason, not only signal lines for transmitting normal-speed signals but also signal lines adapted to transit high-speed signals are placed on circuit boards.
The circuit boards that contain such high-speed signal lines need to provide stringent impedance matching and make provisions for high-frequency noise.
However, the conventional ACF joints allow for interconnection of circuit boards which contain fine interconnect lines but not interconnection of circuit boards which contain high-speed signal lines.